Box for 2 XFL 12s?

I got my XFLs in today and they simply won't fit in my ProBox. They are about 1/4 inch too wide. I would just make the holes bigger, but I don't like how highly tuned the box is anyway (around 40Hz)

What kind of specs would I need for 2 XFLs, and what kind of design? I'm thinking subs and port back, but I'm open to other ideas.

The ProBox *barely* fits in my trunk, and has these dimensions. I might be able to add 2 or 3 inches to the height and depth, but none to the width.
Airspace:
2.25 cu. ft. per side
Dimensions:
W: 36" D: 22.5" H: 14"